Cross-section of a fossilized ammonite shell

© Marianna Armata/Getty Image

Fibonacci Day

It's a bit of a fib that Fibonacci, the 13th-century Italian math whiz, was the first to sketch out a number sequence in which each number is the sum of the two preceding numbers: 0, 1, 1, 2, 3, 5, 8, 13, and so on forever. In fact, scholars in India described the sequence centuries before Fibonacci, and they probably weren't the first to figure it out either. But in any case, each November 23—that is, 11/23—we celebrate the infinite series known as the Fibonacci sequence.

So what does this have to do with our image of a fossilized shell? Try to picture the Fibonacci sequence on a graph. If you properly arrange squares of the areas 1x1, 1x1, 2x2, 3x3, 5x5, 8x8, etc., on graphing paper, a curved line drawn through each square will form a perfect expanding spiral not unlike the ammonite fossil cross-sectioned here. Not every spiral in nature expresses a perfect Fibonacci sequence, but nature does seem to have a thing for spirals. And in that sense the Fibonacci sequence seems especially elegant.